Fig. 1. Schematic of meta-surface structure based on symmetric split rings. (a) Schematic of 3D structure; (b) schematic of unit structure

Fig. 2. Simulated transmission spectra of meta-surface structures based on symmetric split rings

Fig. 3. Field distribution based on a symmetric split-ring meta-surface. (a) Electric field distribution at 0.937 THz; (b) surface current distribution at 0.937 THz

Fig. 4. Equivalent circuit model of meta-surface cell structure

Fig. 5. Equivalent circuit model of the meta-surface sensor covering the object to be measured

Fig. 6. Transmission spectra of meta-surface with the change of analyte thickness h₃ and the relationship between h₃ and frequency shift. (a) Transmission spectra under different h₃; (b) relationship between h₃ and frequency shift

Fig. 7. Transmission spectra of the meta-surface as a function of refractive index n and the relationship between n and frequency shift. (a) Transmission spectra under different refractive indices; (b) relationship between n and frequency shift

Fig. 8. PI and meta-surface transmission spectra of 100 mg/dL furazolidone added dropwise. (a) PI and PI+furazolidone; (b) meta-surface and meta-surface+furazolidone

Fig. 9. Transmission spectra for the dropwise addition of two mass concentration gradients of furazolidone solution. (a) 100-1000 mg/dL furazolidone solution; (b) 10-100 mg/dL furazolidone solution

Fig. 10. Transmission spectra of furazolidone solution in the mass concentration of 1-10 mg/dL added dropwise

Fig. 11. Relationship between frequency shift and furazolidone mass concentration

Fig. 12. Transmission spectra for the dropwise addition of two concentration gradients of furantoin solution. (a) 100-1000 mg/dL furantoin solution; (b) 10-70 mg/dL furantoin solution

Fig. 13. Relationship between frequency shift and furantoin mass concentration